text:
How do aircraft instruments determine the aircraft's orientation relative to the ground?
Autopilots exist for airplanes and drones, how is orientation measured with respect to ground? In particular how is the direction of gravity detected and how is it differentiated from acceleration due to thrust?

This strongly depends on the kind of aircraft you have in mind. Large airliner or small GA aircraft? Analog instruments or digital displays?

Small, maybe even RC sized

Related: How can aircraft determine true north for inertial navigation systems?. In the answer you'll find how gravity is sensed too.

From standard sensors, we can completely determine attitude
Attitude estimation is a mathematically rich domain. If we have sufficiently precise measurements across sufficient degrees of freedom we can completely, and uniquely, solve for the attitude. However, the way any particular application goes about solving it is highly dependent on the goals (autonomous navigation or just keeping the wings level and the nose pointed in the right direction?), so it's no surprise that there are a multitude of solutions, one written by yours truly.
Formal definitions

SO(3)  means roll-pitch-yaw
T(3) means x-y-z, i.e. latitude, longitude, and altitude
SE(3) means the combination of roll-pitch-yaw and x-y-z

Solving for SE(3) means being able to measure/infer both T(3) and SO(3).
Position
T(3) is straightforward, as that easily comes from a GPS-style system, aka GNSS. (Although it could also come from some other ground-based reference system combined with an altimeter of some kind, so it's not restricted to GPS-style sensors.)
Attitude
SO(3) is more complex to get just right, since the reference is to the ground and yet there are no deployed ground-based systems to measure the plane's roll, pitch, and yaw. Therefore, we have to make do with sensors mounted on the moving inertial system, i.e. the aircraft.
Without getting too much into the details, in modern autopilots we typically measure the turning rate with gyrometers and integrate that to get an attitude reference. Because these attitude solutions inevitably drift, we correct roll-pitch with accelerometer measurements, and yaw can be corrected with a yaw measurement such as a magnetometer.
In airplanes, which typically fly in a coordinated manner, we can isolate gravitational acceleration by taking the measured acceleration and subtracting the predicted centripetal acceleration (which in constant-speed flight and at a given bank angle is identical for all airplanes).
Combining position and attitude
It's very helpful to use the aircraft's position to refine its attitude estimation. After all if we hvae a good understanding of the aircraft's flight dynamics-- e.g. airplanes can only fly forward, helicopters can fly any direction, and balloons don't have a well-defined forwards direction-- then we can draw good conclusions about how the aircraft must be oriented. So fusing all these measurements together is how we can come up with a very solid estimate of attitude.
Extensions
Recently, we are also seeing RTK-GNSS (with a precision of several cm) being used to fully characterize an airplane's SE(3) state. This is done by placing the receivers as far apart as possible and using the extended baseline to definitely locate the aircraft's extremities. If we know where the nose, tail, and wingtip are in T(3), then because we know the plane's shape we also know the plane's attitude and position.
The downside is that if the plane rolls over than the antennas no longer have a clear view of the sky, but this can be easily corrected for in the short term by using inertial measurements.
Definitely the sum is greater than the parts.
Appendix
If you are interested in more details, I can refer you to what we did at Tau Labs, a drone autopilot ecosystem which existed from roughly 2011 to 2017.

EKF: theory and code
Complementary filter: theory and code

Please tell us the words accompanying some of the initials you used (eg GNSS, RTK).

That gets sticky. If I spell out GNSS, should I also spell out GPS? GPS is just the American implementation of a GNSS, but Galileo, GLONASS, and Beidou are also equally valid sources. Indeed, we use as many of those satellites as we can when getting a global localization fix. Hopefully we'll stop using GPS to generically refer to all these systems, as it's US-centric.

Interesting point, but I would suspect that most readers know what GPS means but not the other things.  But feel free to spell out what GPS means as well!    Of course there is always google and wikipedia, but...

I added links to wikipedia pages, think that's okay?

I'd personally prefer to see them spelled out at least once, but thanks for adding the links.  Very informative answer.

Note access to the RTK correction network is not free. In Europe it is sold about 1000 €/year.

In analog-instrumented planes, orientation with respect to ground is established by a feature inside the attitude gyro called the erection system which senses the long-term average of the direction of gravity. It then slowly urges the gyro to establish and hold the correct position of the horizon while still indicating short-term excursions from level flight in pitch and roll.
In vacuum-driven gyros, the erection system consists of small air leaks in the rotor support gimbal which are opened or closed by small vanes that are hung so they swing freely under the influence of gravity. When they are open, they apply a tiny thrust to the gimbal which gently precesses or "drifts" the gyro into its erect position in which the horizon line is perfectly perpendicular to the direction of "down" as sensed by the vanes.
The time constant for the erection process is of order ~minutes- that is, it furnishes a multi-minute-long average of the downward direction.

So it basically takes a long term average. Do digital ones exist? Can this be done with a kalman filter?

Digital ones exist but I do not know how their sensor networks function, I do not know what a kalman filter is. -NN

A Kalman filter outputs a best guess by repeatedly using new measurements for corrections of that best guess. Large deviations of the newly measured value aren't fully trusted but only applied partially. They are used to correct for noise in the measurement. If you interpret banking effects as noise, then yes, a Kalman filter works similarly. But there are better ways for attitude measurement.

How do you do it then? Banking effects could be integrated right?

@FourierFlux, yes, this is routinely done with a Kalman Filter. See my answer for a brief explanation and a lot of links. Your instinct is right that, in an airplane, the centrifugal forces arising from banking can be used to refine the understanding of an airplane's attitude.

In the case of the mechanical attitude indicator, a key point in understanding how the drift correction works is that in the reference frame of the gyro platform-- as opposed to the reference frame of the aircraft-- the direction of the g-load compont created by turning is not constant, but goes round and round.  That's why circling in the same direction for hours on end wouldn't "confuse" the instrument.

This is a surprisingly hard problem. Initially, the answer was: Just look out of the window. Of course, this became less helpful when flying in clouds. With unmanned aircraft it has become the hard problem I mentioned.
The usual recommendation for glider pilots who get sucked up into a cloud is: Let go of stick and rudder, open the speedbrakes and hope for the best.
Accelerometers will only give you the combined result of gravity and inertial loads, and only the magnitude of the signal can be used to separate obviously false readings from probably correct ones. Combine them with gyros, a barometer and clever software, and always be aware that both, sensor and software, will not be error-free.
What you do is to use a well-calibrated high quality gyro and do some common sense checking: If the load factor is permanently above 1, don't use that attitude to reset the gyro. Instead, make sure there is enough flying time straight and level for a proper reset and your maneuvering does not take long enough for drift to build up to a significant level. You can even perform checks during flight with a small roll attitude change and then a check how the other parameters behave to establish what is level.

One simple method is that orientation is detected, calibrated, and fixed in place prior to flight. The aircraft can be assumed to be on the ground at systems startup. Gyroscopic instruments are spun up and zeroed while the aircraft is on the ground.

Yes but there exists drift which will destroy absolute orientation.

Also without drift, the gyroscope maintain orientation relative to the universe, but as the aircraft flies, the Earth curves below it and the attitude indicator is supposed to follow it.

The modern solution is to use an Attitude and Horizon Reference System, or AHRS. The system includes both rotation rate sensors and linear accelerometers for all three axes.  In the short term, the rotation rate sensors are the key players, but GPS data and magnetometer (magnetic compass) data is used to help seperate acceleration due to turning or changing airspeed from acceleration due to gravity, to allow the system to use gravity to correct the system for "drift" from various sources and accurately keep track of which way is "up" over a long flight.  This system of correction and calibration means that it is not absolutely necessary to initialize the system on the ground with the aircraft level and stationary, though this step may help the system reach optimum performance more quickly.
Following the principles given in this related answer,  it is possible to create a similar system without utilizing GPS data and magnetometer data to help with drift correction, but such systems invariably require much more expensive (and larger and heavier) components to achieve the same level of accuracy.
Naturally, some military navigation and attitude reference systems are designed to still work in the event that the GPS network is eliminated.


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What information is recorded in aircraft sensor and maintenance logs?
I was wondering what the sensor and maintenance logs in an aircraft look like and what are the values logged? Like maybe the engine temperature, altitude, exhaust temperature, etc. I know the data is logged in the black box, was wondering if it is available to the owner of the aircraft to any cloud service for further analysis or something. I'm talking about fighter planes and commercial aircraft.
I am looking for variables like the speed of the turbine (N1 and N2), altitude, pitch, roll, vertical acceleration, air temperature, exhaust gas temperature, etc. Came upon a Vox video where they showed about 60 variables.

You may be interested in the quick access recorder which is primarily for maintenance purposes. Engines may also have separate logging systems complete with data uplinks directly to the manufacturer...

Modern digital Flight Data Recorders can capture hundreds of channels of data.  Exactly what is being captures is specific to that operator and that fleet, and I don't know that there is any public source document that enumerates everything that "this" type of aircraft at "this" operator is logging.  One example, though, starts at page 6 of this report an American Airlines flight 77 on 9/11/2001, and runs for hundreds of entries.
You can probably assume that at a bare minimum, the positions of the flight controls (stick or yoke, rudder pedals, throttles, flap and gear and speedbrake levers, etc) in the cockpit are captured for every aircraft, along with the positions of the flight controls themselves (each aileron, flap, speedbrake panel, elevator, rudder, etc) and also the indications of at least every engine parameter that the crew can see, probably plus a few others.  Also, GPS position, along with INS position, speed, and acceleration are probably a safe bet; some amount of FMC data such as the active waypoint is probably in there too.  Also the various system inputs like doors open/closed and weight-on-wheels.
One of the best ways to see what's out there in this realm is to go through NTSB accident reports; those often have "traces" of the various data over time, and by looking through that you can see exactly what was being captured on a particular accident aircraft. (For an example, start at page 20 of the AA77 FDR report.)  Or, more likely, you'll at least see a subset of everything being captured.  If the engines were running fine, you may not see extensive logs of normal performance, while if an engine problem was relevant to the accident, there will be more attention on it.
At the most detailed level, the data is captured as ones and zeroes, and how it's displayed afterwards is all a function of what software is doing the playback.  And that, again, will depend on what the military service or airline or investigative body bought & uses.  Again, looking through NTSB reports and briefings, it's common to see animations both of cockpit displays ("so at this point in the flight, the crew was seeing this and moving the controls like that") and the aircraft performance in 3-dimensional space.  The display of traces is a less-enhanced version of that -- various defined data outputs down the side, and time running across the top.
The NTSB report on Atlas Flight 3591 also has various traces starting at page 7 of the linked PDF file; this is a screen shot of the first of those pages:

For the F-35, it captures possibly too much. Not just every aspect of the physical operation of the jet, but all the other things the jet can do.
Capturing details on all the radar and sensors that may be trying to track it, route, speed, altitude, G's etc, etc.
The specific details of what is captured and available for download is not generally public info.
The Autonomic Logistics Information System (ALIS) system is going away, to be replaced by Operational Data Integrated Network (ODIN) in late 2020.
https://www.thedrive.com/the-war-zone/31861/replacement-for-f-35s-troubled-alis-cloud-based-brain-rebranded-odin-and-is-still-years-away

The Pentagon says that a replacement for the F-35 Joint Strike
Fighter's long-troubled cloud-based computer brain is finally coming.
The U.S. Air Force, Marine Corps, and Navy have said that the existing
system is one of, if not the most significant factor in the abysmal
mission capable rates for their respective F-35 variants and a major
contributor to the growing sustainment costs for the aircraft.
Unfortunately, the upgraded system is not expected to be in widespread
use until 2022 at the earliest.

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What is the relationship between fuel mixture, throttle setting and engine temperature?
I'm trying to understand the relationship between mixture, throttle, and engine temp.  In this article from AOPA, it states

... a lean mixture of 16 to 1 is not going to burn as hot as a rich mixture of 8 to 1. ... an engine [runs] hotter on lean mixtures.

This seems in general contradictory but what I'm gleaning is that there are some instances in which a leaner mixture will result in a higher engine temp and other instances in which a richer mixture will.  Perhaps this comes down to throttle?
Could someone clear up for me what are the "primary points" so to speak with regards to engine temp that I should be aware of?
Further, does there exist a general graph somewhere with mixture, throttle, and engine temp on the x, y, and z axes, respectively?  I might expect to see local maxima at full lean, full rich, and stoichiometric and local minima at I don't know where.

This image from Lycomings leaning instructions is likely what you are looking for:

The misnomer may be that leaning always increases the temperature of the engine. If you start at full rich or something above peak lean temp, leaning the engine will cause the CHT and EGT to rise until it hits its peak. If you continue to lean beyond this the temperature will start to drop again, and rapidly, but so will the power generated and at some point you run the risk of simply cutting the engine out so generally you want to lean to "peak EGT" since thats as low as you are practically going to want to go (unless you want worse fuel economy while flying slower).
If you look at the chart you will see below peak EGT your specific fuel consumption will also start to increase again.
Broadly speaking you can also see that increasing the mixture within its general operating range has a cooling effect on the engine.
If you are flying GA planes I would say the primary points in regards to engine temp is simply:

Keep an eye on temps and don't overheat the engine.
Lean slowly and carefully, keeping an eye on EGT or CHT for warm up which may not be immediate while leaning

If the gauge is creeping up, richen the mixture and consider reducing your angle of climb to increase airflow over the engine.

I don’t have the graph you are looking for, but we can reason this out.
If the mixture were 100% fuel and 0% air, it would be impossible for ignition to occur, so the temperature would be at a minimum. This explains what happens when you “flood” an engine by over-priming.
If the mixture were 100% air and 0% fuel, there is nothing to ignite. This is what happens when you pull the mixture knob/lever to IDLE CUTOFF at the end of a flight to kill the engine.
Ignition can happen between these two points, and temperature must rise when that happens, so we have a curve with some sort of peak in between and sloping down toward where the reaction fails on either side.
This peak temperature happens at the stoichiometric ratio between fuel and air. Having more fuel than optimal means you are running Rich of Peak (ROP), and having more air than optimal means you are running Lean of Peak (LOP). In both cases, the excess molecules (whether they be fuel or air) will be absorbing some of the heat and carrying it with them out the exhaust ports rather than letting it do useful work.
Throttle position is irrelevant.

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How does the airflow above an airfoil account for the downward turning-action of the airflow below the airfoil?
Wikipedia provides an explanation of the lift force in terms of flow deflection and Newton's laws, emphasis mine:

An airfoil generates lift by exerting a downward force on the air as it flows past. According to Newton's third law, the air must exert an equal and opposite (upward) force on the airfoil, which is lift.
The airflow changes direction as it passes the airfoil and follows a path that is curved downward. According to Newton's second law, this change in flow direction requires a downward force applied to the air by the airfoil. Then Newton's third law requires the air to exert an
upward force on the airfoil; thus a reaction force, lift, is generated opposite to the directional change. In the case of an airplane wing, the wing exerts a downward force on the air and the air exerts an upward force on the wing.
The downward turning of the flow is not produced solely by the lower surface of the airfoil, and the air flow above the airfoil accounts for much of the downward-turning action.

In what way does the air flow above the airfoil account for much of the downward-turning action of the air flow below the airfoil?

The answer is buried in the linked Wikipedia article if you read it carefully a few times.
In a nutshell, at least in my interpretation, the "zone of suction" you might call it, the Bernoulli effect low pressure region above the airfoil, induces air outside the zone to accelerate toward it; to "fill the void".  On a zone of suction that is moving, like the top of the wing, it means that a large region of the air stream above the wing wants to accelerate toward the zone, which being below, means that the net result is the a large package of air is induced to move downward in response to the wing's passage below it.
Maybe half or more of the total package of air that is redirected downward is above the wing.  This air is being induced to move by "pressure trickery" as opposed to being shoved down directly by the pressure wave of physical wing's passage like the air below.  A water ski works by deflecting only the fluid below it.  A wing works by deflecting the gasious fluid below, and also inducing the gaseous fluid above to join in by careful management of pressures.
This is partly why disruption of the flow above has a more drastic effect than disruption of the flow below - spoilers go on top instead of underneath.  Air below is just being physically deflected; the air above, for quite some distance, is being "coaxed" to be pulled down toward the low pressure region, and if you disrupt the low pressure region, all of the air that was ready to be induced to move down doesn't have to, and you lose most of your Newtonian force reaction.
The result is that this contraption flies fine with all that junk obstructing the flow under the wing, but if you put it all on top, it would never get off the ground.

The tricky part is explaining why the low pressure region is there. You can't you Bernoulli's principle, because you don't yet know there should be higher speed either. The real reason is that air “does not like” to navigate sharp corners, so it prefers sticking to the surface to creeping around the trailing edge—until the slope is too steep, when the wing stalls.

What would be a good shorthand label to use in place of Bernoulli effect?

"Pressure trickery", or "bait and switch", can be used.  The leading edge splits the air flow up and down much like the bow of a ship.  The low pressure area is created because the wing moves past the impact zone faster than the air moves down to close the vacuum.  This phenomena (including stall buffet turbulence) can be observed at the stern of a common boat.  As it moves faster, the turbulence separates from the back and forms a neat "downwash" off both sides, resulting in a "V" wake (that water skiers love).  The vacuum above the wing is formed by the wing outrunning its turbulence.


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Where to get Initial EASA Class 1 Medical?
Can somebody suggest a list of EASA medical centers, where I can get Initial Medical 1?
Any EASA county is OK.
I'll appreciate any links, thank you!
Amendment:
I've found lists of AMCs or at least medical examiners approved by CAA for the following countries: UK, Spain, Serbia, Poland, Finland, Croatia, Ireland, Malta, Switzerland, Romania, Greece, France, Danmark
Full list of EASA countries and list to it's CAAs can be found here. And some of examiners all over the EASA here.
Does somebody know about other countries like France, Germany...? I have not found any lists of AMCs approved by CAA or at least medical examiners for these countries

Which country you want to do the medical?

Edited. Any EASA country

It depends on the country you are going to take the medical examination.
Normally, the national civil aviation authorities of each European country will have this listing. For instance, in Spain, AESA publishes here the approved medical centers where applicants can take their initial and successive examinations.
So I suggest to first find out the authority from your country and always make sure with the medical center that you are going to take a certified EASA Class 1 medical examination.

BTW, in case you are planning to take the medical examination in Spain I strongly do not recommend "CENTRO DE INSTRUCCIÓN DE MEDICINA AEROESPACIAL (CIMA)". The center is run by military personnel and their philosophy is that any deficiency will be used against you to fail the examination. Me and many colleagues have been affected by this :(

There is a list of UK Aeromedical centres is available on the Apply for a Class 1 medical certificate page on the CAA website
(I'll include a copy of it as soon as I've worked out how to post a table here)


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Vintage photo, Seatac airport
I’m spending the night in a hotel at Seatac Airport in Seattle, Washington, USA. The vintage photo below is hanging on the wall of my room. I recognize the airport as Seatac, circa 1950’s. The photo appears to depict some sort of celebration, with all of the bunting and crowds.  I initially thought that it might be a Boeing-related airshow, given the company's Seattle roots.  Plus, the aircraft in the upper-left appears to be a B-17, with a 377 in the upper-right.  But the aircraft next to the B-17 appears to be a Fairchild C-119, which seems to eliminate the Boeing connection.  I'm unable to identify the other aircraft.
I'd like help identifying the aircraft in the photo.  Bragging rights awarded to anyone who can id the actual event.

For context, here's the full image:

The photo was taken on July 9 1949, and depicts the opening of Seattle-Tacoma International Airport by governor Arthur Langlie.

The airport cost $11 milliion and opened free of debt. United
Airlines, Northwest Airlines, Pan American World Airways and Western
Airlines started their regular passenger service at Sea-Tac on the day
of the dedication.
This July 1949 aerial photo shows the passenger terminal on the
airport's opening day. Port of Seattle officials estimated that 30,000
people attended the opening to tour the new airport and inspect
several planes. source

All four airlines are shown in the photo:

The two aircraft nearest the camera are -

N88951 Douglas DC-4 in the colours of Pan American World Airways
N47603 Boeing 377 Stratocruiser in the colours of North West Airlines

To the rear on the right is N88816 Douglas DC-4 from Western Airlines; here the same day -
 source
To the rear on the left is a N37540 Douglas DC-6B owned by United Airlines.

source
The two military aircraft at the rear of the picture are proving far less popular with the crowd than the civil ones! They are a Boeing B-17 and a Fairchild C-82 Packet . The USAF was operating Packets out of nearby McChord Field, which might explain its presence. In fact, you can still see a Packet there today.

Bragging rights well deserved! +1


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What kind of flight-control redundancy does the Tu-204 have?
The Russian Tupolev Tu-204 and variants are reported to be digital fly-by-wire. Are they quadruplex redundant? Do they have manual or analog back-up systems?


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What are these two tail elements of the Avro RJ100?
What are these two tail-side elements of British Aerospace Avro RJ100 and what is their function:

Photo source: Eric Verplanken, jetphotos.net.

I am not sure the image (copyrighted) is compatible with the license of this site (CC-by-SA with attribution)

@DeltaLima Oops! Possibly. Though I don't have any other. Maybe we should brought usage of jetphotos.net photos discussion to meta?

I agree, good topic for meta. In fact, I found three related questions already: This one on copyrighted images. Then there are two on proper image attribution.

@voretaq says best left as is.

@mins You have answered yourself! :> I forgot about this one. Thanks for reminding me this.

The one behind is an aerobrake. The tail opens up to increase drag. It is much better seen in this Wiki image:

The one in front looks instead like the APU exhaust.

Just to expand a bit: ...and the reason to have an aerobrake is to allow for steeper descents. (It also has spoilers like most other airliners). BAe 146 was designed as a short takeoff/landing (STOL) aircraft to serve regional aerodromes in populated areas, and being able to descend (and climb) steeper is an important capability for it.

The one in front is the APU exhaust. As soon as I find the old SRM manual I have I'll add a picture.

Airbrake and APU exhaust, just so.
Some aircraft use airbrakes on the tail cone, instead of airbrakes on the fuselage sides, the wings, or on the fuselage belly. The tail cone airbrake can easily be combined with a brake chute, should one be needed during testing.

what does this add w.r.t. the existing answer?

You should edit your answer to highlight what you add to existing answer.

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What is a vortex generator?
I saw a vortex generator mentioned in an aircraft listing.
What is a vortex generator?

Similar Questions: How does the position of vortex generators on engine cowlings affect flight? and What is this flange on the engine?

Similar, but not the same. This question is very 'google-able'.

To be more general, a vortex generator is a small angled plate installed on an outer surface of an aerodynamic body. The angle of the plate causes the air to swirl, creating a vortex behind it. This effect allows the air flow to remain "attached" to the surface even at points where the flow without a vortex would separate from the surface.
One of the most common uses of vortex generators is on aircraft wings forward of the ailerons. When the aircraft wing stalls, the flow detaches from the wings. This means that the flow will detach before it reaches the ailerons, making them ineffective. The use of vortex generators helps the ailerons to provide control even if the rest of the wing is stalled.

Source
Of course, these also add drag, even when the wing is not stalling, so they are only added where needed.
They are also used in other places, such as the engine, as in Farhan's comment above, and also on the tail of the 737.

I will try to explain the physical mechanism, adding extra information compared to previous answers.
As mentioned before, the vortex generator is usually taking the shape of a plate. What this plate is doing is generating an small vortex. This vortex is basically a region where the flow is rotating around its axis. Basically this plate extracts energy from the flow generating this rotation on the flow.
Ok, this rotational flow has got energy and, if properly oriented interacts with the boundary layer over the wing providing further energy to it. With that extra energy the boundary layer is more resistant to separation, that means, that you can increase the angle of attack further and obtain a higher lift coefficient for the same wing.
Now comes the why?. A vortex generator is always creating drag, always but it might reduce the fuel consumption of the airplane. How?
Think about overall design of the airplane, for a given flying condition the amount of lift generated can be obtained big lift coefficient times wing surface.
Imagine now, that we are designing the airplane and we have found that the condition that is dimensioning the needed size of the wing is, for example, the maximum runway length at take off, in order to reduce it you need to generate more lift at an specific speed. For being able to accomplish that you can either increase the wing surface or increase the maximum lift you can obtain from the wing, and you can accomplish that by introducing vortex generators smartly designed for that condition.
A trade off is later on made between increasing the wing surface (with the impact in drag and weight) and including the vortex generators. So, although adding those vortex generators are adding drag compared to a clean wing, it might be the case that you are actually reducing fuel consumption because the other alternative is adding more wing surface and the optimum solution became the vortex generators.
There are several location of vortex generators, some of the on the vertical plane improving rudder efficiency, others in the upper surface of the wing, others over the engine affecting the slat during take-off or landing.
Another use of vortex is after designing the airplane as quick fix to solve “unexpected issues”.

They're little winglet type things that you install on the surface of the wings to encourage laminar flow of air and to discourage stalls. Think of them as "cheap insurance for when you're not monitoring your airspeed very well".
Edit for future readers: Should be attached flow, not laminar flow. See below comments for explanation.

uh-o - replace "laminar" with "attached" and the answer looks good.

Okay, teach me.  I thought there were two types of flow in a fluid (air in this case) -- laminar and turbulent.  I thought air transitions from laminar flow across the surface of a wing to turbulent (stalled) flow, and vortex generators somehow cause that transition to be delayed.

@Calphool Wikipedia has a good cursory overview, as does the image in fooot's answer. Basically it's the change between "attached" and "detached" flow (the separation point) that matters for delaying the stall, and attached flow can be laminar or turbulent. Attached turbulent boundary layers resist being detached from the surface (wing) more than a laminar boundary layer does, so basically vortex generators delay the flow separation by making the air more turbulent in a particular way such that it's less likely to separate from the wing.

@Calphool: voretaq7 beat me to the right answer. It is basically about mixing flow near to the wing surface (which is slowed down due to friction) with flow at some distance which can then re-invigorate the boundary layer (flow near to the wing surface). If the flow near the wing is slowed down to a standstill, flow separates and the wing loses some of its effectivity. If you ask a new question, I will explain it in more detail than is possible in a comment.

@Calphool: Laminar and turbulent are the two types of boundary layer, a thin, almost microscopic, sheet of air close to the surface. Attached and separated flow is another concept (and the one which vortex generators address) which concerns the macroscopic flow pattern around bodies. Vortex generators will make sure that the boundary layer behind them is turbulent, so that is the reason for my first remark.

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Did B-17 gunners beat on the wings of other planes in their formation?
I am certain my father, a B-17 pilot, told stories about his gunner having to beat on the wing of another plane in the formation with the tip of his gun to get the pilot to pull away and avoid a mid-air collision. Anyone have a similar story? Do you know which gunner?

What does"beat on the wings" mean?  My grandfather was also a 17 pilot and he never mentioned that, ever.

As in, they were so close in flight that the gunner could reach out and touch the other plane's wing? I strongly suspect that your father was pulling your leg, because if the planes were that close, then the collision was already in progress, and no amount of beating on the wing would do anything to stop it at that point.

Don't think that they would notice your gentle tapping... If I was in the turret and another friendly aircraft was closing in I would send a blast of tracer across his nose to get his attention..

I'd hate to be the wing-tip gunner assigned that responsibility!

That'd be a roughly 1 meter stick you've got to beat that other aircraft with, at most. Not a long stick at all.
By the time the other aircraft got that close a collision would be unavoidable. Not only would momentum carry them closer, but the banging would likely not even be heard by the crew of the other aircraft.
Remember they'd be wearing headphones, not just for the intercom but even more important for hearing protection. A B-17 is a LOUD aircraft when you're flying it.
Also, by the time you'd get that close the crews of both aircraft would have been screaming at their respective pilots for some time to ask them what the hell they're thinking getting that close to another aircraft.


text:
How are go-arounds safe with close parallel runways?
Some airports operate simultaneous take off and landing on parallel but close runways. By close, I mean like the pairs of runways at LAX.
What if a landing aircraft makes a go-around at the same time as another aircraft takes off? How is separation maintained? Would it be enough for the missed approach procedure to specify turning away from the departure runway?

It's just like a normal go around.  You just stay in your traffic pattern.  At Riddle, we would do go arounds all the time, and it was never a problem.

Its not just parallel runways, but also intersecting runways as well. SFO uses 28s for landing and 01s for (most, non-747 and non-Asia) departures. When there's a go around on 28, the controllers will hold the 01 departures until the go-around is complete. Typical go-around on 28 will be "Present heading, climb and maintain three-thousand, contact approach 135.1"

There are also ILS/LDA and GPS/RNAV PRM approaches into SFO's 28R and 28L which are worth reading if you want to know about missed approach procedures for closely spaced parallel runways http://155.178.201.160/d-tpp/1411/00375PRMAAUP.PDF

The first thing I would point out is that LAX isn't going to be running simultaneous approaches on 24L and 24R or 25L and 25R. They'll select one of each of the parallel sets for the landing runways (typically the outer runways), and one of each for departing runways (typically the inner runways). For example, they might be landing on 25L and 24R and departing 25R and 24L. So, there's quite a bit of distance between those runways, and very little risk in a go around situation.
Here's a diagram illustrating LAX's typical arrival/departure runway usage to make it more visually apparent what I mean:

The second part of your question about an aircraft taking off at the same time as a go-around certainly happens, and when it does, ATC needs to take action to ensure safety and separation. ATC separation requirements can be satisfied by altitude, distance, or divergence (and, in some cases, visual contact). In the situation you described, divergence is the quickest and safest way to achieve separation. I believe the requirement is 30°, so tower would typically order a go-around and order a new heading at least 30° off of runway heading. The geography of the area, layout of the airspace, and the approach patterns would likely dictate the exact procedure used at each airport since their two primary goals, in order, are going to be 1. safety, and 2. getting them back in the approach sequence.
In the LAX example, a go-around on 24R would most likely get a right turn, and 25L would most likely get  left turn (away from the airport) so as not to conflict with other departing or arriving traffic. This is one of a few reasons the outer runways are preferred for landing.

while true for a civilian airport, military airports with multiple training runways are different (e.g. a undergraduate pilot training base), as 3+ runways may be in use simultaneously

Don't know about the exact procedures at LAX, but often the departures on closely spaced runways are not independent from the arrivals. I.e. the take-off clearance will not be given at moments that a go-around on the other runway would cause a nasty separation conflict.

@SSumner At ATL, 5 runways are used simultaneously.

@reiab - yes, but don't they alternate departures/arrivals on the runways? At AF bases, you have departures and arrivals simultaneous on all 3 runways

Adding some more information to Bret's answer:
Take a look at both ILS approach charts for Munich's runways 26L and 26R1, which are parallel runwawys. Both ILS instrument approaches terminate at the Missed Approach Point (MAPt).
You can see from the charts that the Missed Approach for the northern runway 26R mandates a right turn to the MIKE (MIQ) NDB after passing 1.0 DME of the Munich (DMN) DME.
You can see from the charts that the Missed Approach for the southern runway 26L mandates a left turn to the Munich (MUN) VOR after passing 1.0 DME of the Munich (DMS) DME.
In the event that you have an arrival to the northern runway and a departure from the southern runway that would use a northern Standard Instrument Departure, such as the ANKER6S Departure, you could instruct the aircraft on the departure to maintain runway track or continue on a heading to establish separation between both aircraft.
Tower and Approach controllers develop a contingency plan when working with arrivals and departures in their head, which they can quickly deploy to establish and maintain separation by using standard procedures or vectors.

1The source I am providing here is a simulation resource. While the charts are as close to the real-world counterpart as possible, they are not to be used for real-world aviation, but will serve their purpose for visually supporting the answer and are easily accessible.

Also a big Problem exists at Zurich Airport where they must wait until a Landing on 14 is completed before they can give start-clearance on 16. This is due to the problem if an Airplane wants to land on 14 must make a go-around and the plane on 16 starts simultaneous, a possibility of a conflict can occur in mid-air.

Edit clarification according to my comments:

Normal Route is that Airplanes taking of on RWY16 (they changed it
  slightly on march 2014) have to turn left, Zurich is famous that a
  plane taking off on RWY 16 will fly over the Airport at a much higher
  Attitude :
Out of a Pilot Briefing: All SID out of runway 16 describes shortly
  after airborne a left turn to avoid noise emissions over the city of
  Zurich. This procedure often causes difficulties because it is hard to
  integrate in the FMS. Therefore, we recommend you to fly that left
  turn manually or with the heading function of the autopilot. Take
  caution to not turn right! The SIDs out of runway 34 is more or less a
  long left turn and normally no problem for the FMS. Stay on the Tower
  frequency until advised.

authors: بیژن یاورزاده


text:
What is this airport outside of Cairo, Egypt?
Out to the east of Cairo, Egypt, is a large two-runway airport that Google Maps calls "Capital Cairo Airport" or "Capital International Airport". Here's a link. However, I can't find any information about this airport or what it's used for. Cairo has a major international airport within the city, here, so I'm confused as to what this large airport only 30-40 minutes away is.
As far as I can tell, it doesn't appear on Wikipedia's List of airports in Egypt, and satellite view shows no planes parked at this airport. Satellite view history in Google Earth shows that two years ago, the airport only had one runway, but since then the second runway was added. So apparently this airport was important enough to merit two runways, both over 10,000 ft. Why? What is it used for? Does anyone know?

30°02'52.55" N  31°49'55.05" E

The geotagged photos Google supplies seem to indicate this might, maybe also be called "Katameya Airport." A search on that is very sparse on English-language details (or I'd post this as an answer), but does seem to indicate a dual-use military/civilian airport here, under construction. It's unclear exactly what the current status of the project is, to the extent I can't be positive we're talking about the same place, but a few sources (e.g. this one) indicate as such.

It's apparently identical to another new airport. Seems like it's good to be in the airport construction business in Egypt!

Katameya International Airport, ex-military.


text:
Does an F/A-18 require a lot of rudder in turns?
I am an aspiring Navy fighter pilot and I use an X-Plane add on for FA-18 Hornet as a fighter. It's made by a creator named Colimata. I think the turns are unrealistic. When I begin a bank a lot of rudder is required to keep coordinated. Does anyone know if this is realistic?

No that doesn't sound at all right.  Pretty sure the F-18's digital flight control systems include a yaw damper functionality so it's hard to see how you would have to center the brick/ball with rudder; the computers should be doing it.  You should probably try the DCS F-18 which I have heard is a pretty realistic one.

Eagle Dynamics has a pretty detailed F/A-18 module within their DCS product, you may want to give that a try. That sim does represent a pretty efficient yaw damper, as John K points out; the rudder is rarely touched outside of cross-wind takeoffs and landings.

You likely need to enable the Yaw Damper on the autopilot controls.

I used to be an avionics instructor teaching maintenance type courses for the F/A-18. I have plenty of hours flying in the simulator where I would get the students to conduct navigation flights to familiarise themselves with the operation of the instruments as well as flight controls. I can confirm 100% that the rudder is barely touched once airborne. There is no need to co-ordinate turns as the flight control system does it for you. These things are incredibly easy to fly. It is the controlling of your radios, weapons, FLIR, navigating and keeping an eye on the RADAR all at the same time that is the hard part.

Rudder isn't required or used for most flight operations.
This is true of most turbojet aircraft, too.


text:
How are carrier landings graded?
I'm an aspiring naval aviator (preferably a Hornet or an F-35) and a DCS player. Here's a question for any former navy aviators or LSOs. What would get you a good or bad landing grade on the carrier? What would the desirable landings look like?

On the ball, catch the third wire.

Yeah; 3rd wire best, 2nd wire next, 4th wire next, 1st wire very bad.   Fantail, that's the end of that. Anyway, you're thinking a bit far ahead aren't you?

To paraphrase GySgt Foley from the movie An Officer and a Gentleman:   “My grandmother is an aspiring Naval Aviator!”
Anyway, I am a former LSO, and I pulled out my old LSO NATOPS manual to see if I could find book definitions of the criteria for each grade.  I can’t seem to find them, but they are as close to verbatim as I can remember as described in the answer here.
Worth noting, the grade is not always about the wire you catch.  In other words, OKs aren’t limited to the 3 wire, you can still get an OK for a 2 or 4 wire.  It all depends on how and why you got that particular wire.  For example, if you get low, just miss the ace and taxi into the 2, that would likely be a "No-grade".  However, if you fly a sweet pass and dip just enough at the ramp to barely scoop the 2, that could still be an OK.  And anything in between is probably a "Fair".
The same thing would apply to being way long and just barely grabbing the 4 to avoid a bolter, vs just barely missing the 3 after an otherwise solid pass.
Really though, the question is not really answerable in a useful manner to a lay person.  Judging any “sport” is subjective, and often the LSOs don’t even agree on a grade.  After watching literally thousands of landings over a few years and being mentored by senior LSOs you just develop an eye and a feel for what a good pass and bad pass look like.  (and there are always plenty of “tweeners” to argue over!)
It really boils down to subjectively assessing the duration and magnitude of the pilot's deviations from perfect, and the appropriateness and timeliness of corrections.  In other words. how much the airplane is "moving around" out there...


text:
What triggers a CVR to start recording?
Until recently, I was under the impression that CVRs will start recording as soon as the engines are started and turn off when the engines are stopped.
However, this is not the case given there are only 2 hours of recording time.
In one airplane disaster documentary, the CVR started recording at the gate and when the plane was getting de-iced.
So when does a CVR start recording, is this something that is started manually?

Related: https://aviation.stackexchange.com/q/78605/35166

The CVR (and FDR) are continuously recording while the aircraft is in operation. In the days of magnetic tape, this was done with a continuous loop. In digital systems, the same is emulated by automatically returning to the start of the storage area whenever the end is reached. In both cases, the new data always overwrites the oldest data, so the last N hours is always available. When there is a crash, investigators locate where along the loop the accident occurred, and then read all the way around the loop (physical or virtual) until they reach the accident again.

Okay, now I am a bit confused.
Assuming I take a flight from New York to Hong Kong which lasts about 12 hours, and if an incident occurs leading up to a accident then that gets erased or recorded over?
I find it strange that only two hours of recording is available.
But I get it, and as I have read on another thread, people were referring to privacy concerns and so on.
Thanks for explaining this and helping me understand the process.

@Asynchronous - That was pretty much my understanding as well. If you are on a flight from Houston to Hong Kong that lasts 14 hours (realistic in my experience), only the last 2 hours of flight time prior to the electrical system of the aircraft being disconnected or destroyed is recorded. That means that the last 2 hours of the incident is recorded and the rest of the flight is overwritten. Two hours is a long time in an emergency. Radio & telemetry recordings can supplement that time. But, 2-3 hours should give investigators enough data to start piecing things together. Read an NTSB report

@Asynchronous That is correct. Most accidents end within a matter of minutes, so even 2 hours is probably overkill.

"The disappearance of Malaysia Airlines Flight 370 demonstrated the limits of the contemporary flight recorder technology, namely how physical possession of the flight recorder device is necessary to help investigate the cause of an aircraft incident. Considering the advances of modern communication, technology commentators called for flight recorders to be supplemented or replaced by a system that provides "live streaming" of data from the aircraft to the ground" - no company wants to literally air their dirty laundry. Presumably the same reason why body cameras last thirty seconds.

And even if (@DeanF.) stuff started to go wrong before the 2 hours, there would still be a lot of information on the CVR.  The crew may well repeat important points  anyway; if they're trying to deal with an issue for a long time they're likely to recap the critical points periodically. In addition it's unlikely they would be unable/fail to communicate for all that time anyway (though global coverage isn't perfect for all means)

They haven't upgraded the recording capacity once they went digital???

There actually have been incidents where key moments happened long before the end of the tape. Here's a contrast. Flight 232 is a case study in managing a disaster. Key parts of the flight were lost because the tape had limited capacity. On the other hand, the sinking of the El Faro gave investigators hours and hours of bridge recording, which gave the NTSB a nuanced understanding of why a ship would sail into a hurricane.

@LorenPechtel If longer recording times were of benefit to crash investigators, regulators would have mandated it by now. Instead, the industry has used the added capacity to record more data points more often, because that actually does benefit investigations.

So what happens when the critical incident occurs early in the flight but isn't noticed until much later?  A famous (spaceflight but still relevant) example of this would be the Space Shuttle Colombia, which experienced unnoticed damage to the tiles during liftoff that resulted in the shuttle's destruction on reentry.  It's possible this sort of thing could happen to regular aircraft as well.

@StephenS -- the NTSB relatively recently issued a recommendation for longer CVRs due to frustrations caused by long-winded mishaps, as well as some data preservation issues.

@LorenPechtel -- AIUI, that was when the 2h requirement (vs 30mins) started coming into play, but we can do far better nowadays :)

CVRs are normally active as soon as one of the basic electrical buses, like the battery bus, or emergency bus, is energized. So if the airplane has a BATTERY MASTER switch or similar, it is recording audio as you as you switch it on, so pretty much as soon as you climb in and start getting things ready.  CVRs will include a G switch to stop recording in a crash since they record on a continuous loop (most newer ones are 2 hours; older ones 30 minutes) so it can't overwrite the 2 hours prior to the crash if it survived and kept running.  They also normally have an ERASE button that the pilot can theoretically push, but he/she would be in a heap of trouble if they pushed it without some really compelling reason if an incident occurred, and some airlines may have specific policies on when they can be erased.
Flight Data Recorders, on the other hand, are not started up until some action prior to engine start is initiated, typically when the red Rotating Beacon is activated, which is a standard sign to folks on the ground that you are getting ready to start.  On the CRJs, the FDR starts with Beacon, Strobes, or when Weight off Wheels in case you forgot both of the other two somehow, and I'm pretty sure that is typical.

Do FDR stop recording if engine fails?

No they are normally powered by a battery bus, essential bus, or emergency bus and will be one of the basic services powered by a battery power no matter what.

If the pilot pushes the erase button when shutting the plane down after an uneventful flight, nobody should ever notice, no? As I understand it, the company is not allowed to read the CVR anyway. so if the pilot pushes it during shut-down and somebody finds out, it will be the company who will be in trouble.

You brought up an interesting point.  I was with a private operator and we weren't supposed to use the erase button and maybe I made too much of an assumption based on that.  I know that ALPA has a policy that pilots should be allowed to use it after a flight with no incidents, but I am pretty sure a lot of airlines forbid erasure.  I modified my post a bit.  Thanks.

@JanHudec It would probably depend on how they found out. Another crew member could report seeing them do it. I figure the “no erase” rule arose from the incident on TWA841 (1979) where the aircraft had plunged 34,000 feet and the captain erased the CVR when they landed. That caused controversy as the NTSB decided he was covering up evidence of wrongdoing by the crew.

@TomMcW, ok, I see how getting into habit of erasing it after the flight might lead to inadvertently erasing even when something did happen and the record shall be preserved, so they wouldn't want that. (By the way, it's strange that TWA didn't discontinue that flight number after earlier fatal accident on flight of the same number).

By legal requirement, the CVR must be operated from the start of the first checklist (typically Cockpit Preparation or similar checklist), until after the reading of the final checklist.  The CVR can only be erased when the parking brake is set.
If an incident occurs, some aircraft have a marker button on the instrument panel to mark the event, and the CVR circuit breaker will be pulled to preserve the recording, under certain circumstances.
Length of CVR recording may be as little as 2 hours, but most are typically 6+ hours and digital, now.  They include area microphones to pick up cockpit sounds such as switches, alarms, etc, as well as microphone channels for the captain and first officer.
Regarding a mishap on a 12 hour flight: if the mishap is severe enough to warrant CVR review, the flight isn't likely to continue for another 6-10 hours; it's probably going to be an air turnback to the point of departure, or a diversion to a different airport.
A mishap in which the CVR will become significant will occuring up until the CVR can no longe record (a crash, for example); the CVR isn't being over-written, because it's no longer recording.  The CVR records up to the final moments.

I agree with you for airplanes, which is the point of the question. It's worth noting that ships have longer recording periods. Having 26 hours of data was extremely helpful in investigating the sinking of the El Faro.

Note that the FDR also has a longer loop, generally longer than the aircraft endurance, so that one will have the complete flight.

I've been out of it a while, and wasn't aware they are up to 6 hrs.  Cool.


text:
What rules allow a student pilot to add oil to an airplane?
A private pilot oral exam guide I'm reading asks a basic question about an issue I had taken for granted:

You have just completed the first leg of a long cross-country and notice that the oil level is approaching the one quart low mark. As a private pilot, can you add the quart of oil yourself or is a mechanic required? (See 14 CFR Part 43)

Clearly this must be preventative maintenance? No. 14 CFR Part 43 Appendix A does not explicitly list adding oil as preventative maintenance.
Searching online I found a lot of forum posts discussing this issue, some suggesting it is "obviously" preventative maintenance per the definition, but 14 CFR Part 1 does not define preventative maintenance, and others suggesting it isn't maintenance, it's servicing, but this isn't defined either.
How does this work if you're a student pilot on a solo cross country? If you shut the engine off and check the oil, are you stuck if the oil is low?
The best answer I can find is adding oil is not "maintenance" or "servicing," it is Normal Procedure per the Pilot Operating Handbook / Information Manual. The Cessna 172S POH as part of the preflight check on page 4-10 states:

Engine Oil Dipstick/Filler Cap -- CHECK oil level, the check dipstick/filler cap SECURE. Do not operate with less than five quarts. Fill to eight quarts for extended flight.

The POH is a little ambiguous how much oil to add, but it clearly states the pilot executing this procedure should add oil.
I believe this how a student pilot can add oil to a plane, or at least a Cessna 172S. Is this correct or is there a better explanation?

Beides the discussion if this is maintenance or not, I don't think the question would address trainees, but assume you passed the license and ask  behavior in that case.otherwise it would ask for "can a no licensed guest top up lubricants" or such?

[student pilot on a solo cross country] Is that a thing? Am I ignorant in my impression that no student is allowed to fly solo? Or is it understood that this always means "solo with instructor" and I'm the only one who doesn't know that?  :,)

@zedmelon At least in the USA, students are required to do actual solo (by themselves) cross country time.  The flight planning is under instructor supervision of course, but the student must make the flight alone.

@BrianKnoblauch: wow, never would've guessed (I'm more of an AviationSE lurker/enthusiast than knowledgeable resource).  No doubt a student's solo flight is near the end of training--and no doubt parallels between pilot's license and driver's license are limited at best.  That's gotta be such a kickass thrill!  Thanks for the clarification.

The FAA doesn't consider adding oil to be maintenance. The Hochberg (2016) interpretation says:

The subject of adding oil is often debated; however, we note that it
is not an item included in part 43, appendix A, paragraph (c), which
lists items the FAA considers to be preventive maintenance.

Also see the FAA's Flight Standards Information Management System, under Elements of Maintenance (emphasis mine):

In broad terms, it has been generally upheld that basic servicing
tasks, such as fueling and adding oil, are neither maintenance nor
preventive maintenance. But even that has some caveats. When adding
oil requires a precise sequence of steps or partial disassembly to
gain access, then that would be considered a maintenance activity.
Adding oil to an oleo strut for example, would be a maintenance
activity, whereas adding a quart of oil to a GA aircraft would not.

Since adding oil isn't maintenance - at least not in a simple GA aircraft - part 43 is irrelevant and there's no requirement to have any type of certificate to be allowed to add it.

The Hochberg memo clearly states, "None of the tasks you referenced would be required by§ 43.9(a) to be entered in the maintenance records of the aircraft because, under the circumstances you described, they are neither maintenance nor preventive maintenance... The subject of adding oil is often debated; however, we note that it is not an item included in part 43, appendix A, paragraph (c), which lists items the FAA considers to be preventive maintenance." This is the clearest answer here--changing the oil is not preventative maintenance. Thanks!!

The FAA allows pilots to do maintenance themselves. It’s outlined in the following doc from the FAA as well as the full regulation here. I would say engine oil falls under:

Lubrication not requiring disassembly other than removal of
nonstructural items such as cover plates, cowlings, and fairings.

Ah, but this is the crux of my question. If adding oil is preventative maintenance, then you must hold at least a private pilot certificate in order to add oil. Which would mean a student pilot cannot add oil to an airplane.

@moof2k: As some point the PTC's authority will kick in.

@moof2k A student pilot can perform preventive maintenance (43.3(g)) but you still need a private pilot to approve the return to service afterwards (43.7(f)).

Thanks @Pondlife great find. So for example a student pilot could replace a landing light so long as a private pilot approves their work afterwards. A student pilot could not replace a landing light while out on a cross country solo.

I can't find a reference to link, but in the transport world, adding oil comes under the category of "replenishment", and is the same as adding fuel or topping off a reservoir that is crew-accessible.
Many corporate aircraft have oil replenishment systems for servicing engine oil, intended to be usable by the flight crew.  On the CRJ regional airliners and Challenger corporate jets, the system has an oil tank and pumping setup in the aft equipment bay allowing the engines to be topped up by opening the belly hatch and standing in the opening to work the system.
Although flight crews can use the system, the operator management may discourage its use, or the crews themselves may prefer to get mechanics to do it (fear of getting uniform dirty, or risk of messing up the procedure, but in the corporate world you will find yourself having to do that sort of thing because you are in the middle or nowhere with no help available).
As part of your checkout for the 172, instruction on when and how of adding oil, and the operator's policies on replenishment, should be included. The POH says between 5 and 8 quarts, so you're good to depart with anywhere between 5 and 8. The engine will run fine on as little as 2 quarts (that's the minimum safe quantity in the sump to prevent un-porting during maneuvering - plus another half a quart in the oil lines and cooler, and the
rest of the oil is essentially acting as a heat sink) and as long as the temperatures are in limits, in the short run the engine doesn't care how much oil is on board as long as the pickup in the sump doesn't un-port (long term is another matter).
It's useful to know the engine's oil consumption to be able to anticipate how much is enough for a trip. A lot of owners find the 0-320 tends to dump oil out the breather above 6 or 7 qts (the old O-290/O-235 family was much worse for this due to its breather outlet location), so an operator may tell you not to fill above 6 or 7 qts (If the engine burns a qt in 10 hours, that's at least 2 refuelings before you get to minimum oil even if you dispatch at 6, and the engine won't actually blow up on you unless you get down below 2, so you effectively can't ruin an engine with normal oil consumption even if you dispatch with 5 on board and go on a maximum range trip).

bring on the electric plane!


text:
What is this thing on a FDX MD11 (MD10?)?
I assume something forward looking; not sure why there and how they got this to play nicely with radar

Is this the only photo you have of it? It looks like a birdstrike from here.

why was there a military bloke standing around at fedex ?

@Fattie I believe that is the governor of New Hampshire, Chris Sununu, speaking, likely receiving a shipment of medical supplies to fight COVID.  (Based on the seal on the podium, and a quick google search for the NH governor and extrapolating to current events.)  The uniformed officer is probably part of the National Guard or maybe his protection detail.  This is just a guess though.

thanks for that @DarrelHoffman

It's the infrared sensor for the Enhanced Flight Vision System (EFVS).
From FedEx Newsroom June 23, 2008:

FedEx Express is the first major commercial carrier in the airline
industry to receive a Supplemental Type Certificate from the FAA for
the advanced system, authorizing its installation in the company’s
fleet of Boeing MD-10 freighters. The company’s goal for the system is
to improve the level of flight safety by increasing visibility of
pilots during adverse weather conditions and darkness.
A unique application of Honeywell International “Head Up Display”
(HUD) technology combined with infrared “Enhanced Flight Vision
System” (EFVS) technology of Elbit Systems of America Commercial
Aviation-Kollsman Business Unit, positions the system as the leader in
the avionic visual technologies market.
The Honeywell HUD interfaces with aircraft navigational and flight
data systems in presenting a high resolution liquid crystal display of
critical flight guidance information. This is overlaid with real-time
EFVS infrared video of the outside world that is displayed in an
overhead unit in the captain’s forward field of view using
state-of-the-art HUD “combiner” technology. Elbit Systems Ltd.,
Electro-Optics-Elop manufactures the combiner glass.

The combined image appears like this:

Source: FedEx

I was wondering, is that a "your head moves and it tracks your head/eyeballs and paints appropriately" type of HUD, or is it the type where you "have to keep your head in the correct spot" ??

It's a fixed combiner glass.  The pilot adjusts the seat to put their head within the 'eyebox' so that the projected image aligns with the outside world.  It does not try to track the pilot's head or eyes.

thanks for that explanation, good one

@Fattie, HUDs have, generally, been properly aligning with the outside, passively without tracking anything, since their beginnings as reflector sights in 1900! The mechanism is fairly simple: the display is projected to infinity using lenses and the adjusted image reflected off a half-mirror that is the screen. That way the image is properly aligned from anywhere it is visible, so the pilot just needs to keep their head in appropriate range, but not exact spot.

@Fattie, … note that the collimator is needed so that both the real world in the distance and the HUD image are seen sharp by the pilot. If the pilot was just looking through a semi-transparent display, they'd either see the distant objects sharply or the display sharply, but not both at the same time as one would be out of focus. This is fixed by projecting the image to infinity – with the nice bonus of providing the alignment.

@JanHudec got you now and thanks!


text:
When does the mandatory minimum climb gradient during an Instrument Departure Procedure end?
While studying FAA's Instrument Procedure Handbook, I noticed these minimum performance requirements for obstacle clearance, when a SID or ODP is absent for a particular runway:

-- Cross the departure end of the runway (DER) at least 35ft AGL.
-- Climb to 400ft above the DER before turning.
-- Maintain a climb of at least 200ft per nautical mile (FPNM) until reaching minimum IFR altitude.
The minimum IFR altitude is 1000ft above obstacles, or 2000ft in mountainous areas.

I was wondering if the last rule, regarding a constant climb with a minimum climb gradient of 200 ft/NM (if no other is specified) until reaching minimum IFR altitude, applies also in case of SIDs, or it is up to pilot's or ATC's judgement to establish a minimum climb gradient for a particular, arbitrary portion of the SID route.
In other words, if for a particular SID it is mentioned "climb gradient of X ft/NM until Y altitude", then after reaching Y altitude is the pilot allowed to fly with whatever climb gradient he deems necessary, even if it is less than 200 ft/NM?
p.s. I have to give some credit to this question, though it is not a duplicate since it asks if a minimum performance applies in case of the absence of a SID or ODP. I am asking if a minimum performance (especially the last rule regarding the minimum IFR altitude) applies when the pilot is following a SID.

I believe that now I am able to provide an answer to my own question.
I think that the "minimum of 200 ft/NM" rule applies during the whole climb phase. In other words, until the end of the SID, where either the enroute phase begins or the SID itself provides some enroute transitions as a passageway to the enroute phase.
FAA's TERPS manual clearly states:

Chapter 2, "Sloping OCS" 2-1-4b. The concept of providing obstacle clearance in the climb segment of an IFP is based on the aircraft maintaining a minimum climb gradient. [...] The minimum climb gradient that will provide adequate ROC in the climb segment is 200 ft/nautical mile (NM), unless a higher gradient is specified.

In addition, the rule is also repeated in the PBN manual:

Chapter 1, "Common Criteria" 1-3-1g(2). Climb Gradient (CG). Obstacle clearance in a climb segment is dependent on the aircraft maintaining a minimum CG to a specified altitude. The minimum CG (also referred to as standard CG) is 200 ft/NM.


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How does the location of a propeller affect an aircraft's stability?
Some aircraft possess propellers on front of the fuselage, like the Cessna 172, and some aircraft have propellers located at the rear of the fuselage, like the Velocity 173RG-E.

How does the propeller's location affect the aircraft? Why don't we see back-propeller planes more often than front-propeller planes?

Tradition? Birds have their tails at the back. After the Wright Brothers mid-engine rear twin prop plane, the tails moved to the back for better vertical control with the knowledge designers had at the time.  Also more propeller clearance. The props do not move closer to the ground on take off and landing with prop at the front vs at the rear.  Also, the props have less disturbed air to bite into at the front vs at the rear.

A rear propeller will put asymmetrical thrust on the aircraft unless it is perfectly in line longitudinally with the center of gravity in a similar fashion that the engines mounted on the wing can do on a multi-engine aircraft. Research the Cessna 336/7 or any other pusher prop with a high-mounted engine. But, that does not necessarily answer the stability question. Going off of memory, there are other pusher aircraft that have had stability issues if the center of gravity got behind or too close to the center of pressure. Having the thrust line behind the COG may have exacerbated things.

related

Cooling the engine is a bigger problem in rear-facing (pusher) engine designs.

This related question has more info, particularly this answer.

There is a misconception that putting the prop at the back is destabilizing in yaw/pitch, like you were pushing a car as opposed to pulling it.  That only applies if the thrust element has a flexible connection to the body it's pushing/pulling.
When rigidly connected, the thrust axis is the same at any location along the plane's length and has no effect on stability.  All that matters is how far the thrust axis is from the center of mass where it passes by.  If the thrust axis is above the center of mass, power will make it pitch down whether the prop is forward or aft, and vice versa for a low thrust line.
Beyond that, the location of the engine/prop can have inertial effects related to the mass of the engine relative to center of mass, and gyroscopic propeller effects that vary because of the different location of the precession source, and the tail pusher can actually have enhanced stability due to various aerodynamic factors like an effective fin area increase due to the extra surface area of the engine/prop aft, but the actual placement of the thrust element on the longitudinal axis is not part of it.
Engine/propellers are usually on the front because it resolves so many design compromises much more readily.  Pushers are tail heavy when unloaded, which is a big problem (tail pusher jets have to have their main gears farther aft than optimal for takeoff and landing so they don't tip back when unloaded, which requires a larger horizontal tail to provide downforce for rotation).  The prop is subjected a lot more to junk thrown up by the wheels.  Aluminum propeller blades can suffer from corrosion from carbon in the exhaust. All sorts of little problems present themselves, that go away if the engine is at the front.

That's not all. With props, the thrust line changes with the angle of attack. (Simply speaking, a tilted prop deflects the flow to some fraction of its tilt angle). This creates a fairly strong stabilising effect (in pitch and yaw) for pusher props, and destabilising one for tractors (which is quite counter-intuitive: it doesn't just negate the misconception you mention, but works against it). It's a bit involved to explain the cause of this effect and I don't have time to write an answer now, but this one links to a relevant paper.

@Zeus Interesting data. Thanks!

The side area of the prop also contributes to stability in the same way as a fin or horizontal stablizer. At the front it destabilizes so the tail surfaces have to be bigger, at the back it stabilizes so those surfaces can be smaller.

My answer only was intended to address the location of the thrust element when rigidly attached to the airframe; the horse in front of the cart vs behind it.  An increase or decrease in weathervaning tendency due to the area and aerodynamic effects of the engine/prop forward is another issue, and in any case is the misconception is the opposite in that the rear engine is thought to be destabilizing (horse pushing the cart).  Let me make some revisions.

A rear-mounted prop stabilizes the aircraft in pitch and yaw, much as an additional tail, but without control surfaces. Especially for a fighter aircraft, this is the opposite of what you want. THAT is why almost all high-powered, singe-engined aircraft have their propeller in the front: Maneuverability!
The stabilizing effect increases in proportion to the propeller surface area and the thrust, of course. Since a regular airplane needs to have basic stability with the engine running at idle, any additional stability change due to propeller placement comes on top. At full power and with the long lever arm of a single pusher prop on a central fuselage (think LearAvia Learfan), the aircraft becomes stiff as a brick. A two-boom layout (think Saab J 21) is better, but creates additional friction and interference drag, so the advantage of the pusher arrangement is reduced. Note, however, that studies of a tractor engine variant (Saab J 23) showed inferior performance to the pusher design.
If you want hard data on that: There is an old NACA report (NACA TN 2586) on this by John L. Crigler and Jean Gilman, called Propellers in Pitch and Yaw.


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What is the German / European equivalent of FAA Order 7110.65?
FAA Order 7110.65 prescribes air traffic control procedures and phraseology for use by personnel providing ATC services in the USA.
Which documents regulate these aspects in Germany, or, more generally, in Europe?
Please provide also the valid versions of these documents as of the 1st of April 2020.

The „handbook“ for ATCOs in Germany (!) is the MO-ATS (Manual of Operations for Air Traffic Services) which is an internal DFS (Deutsche Flugsicherung - the German ANSP) document and therefore not available to public.
However it is based on the German AIP and ICAO DOC 4444 which are both available to public. For the international legislation check Milo Morkus’ answer.
In the German AIP phraseology examples are found in AIP ED GEN 3.4 Communication Services

There is nothing like a "handbook" for ATC procedures and phraseology for use by personnel providing ATC services in EU states.
There is a civil aviation authority (CAA) in each country of the EU. EASA (EU AVIATION SAFETY AGENCY) provides its own regulations for flying in EU airspace.
The EU standards are "regulated or guided" by ICAO documents and annexes.
ICAO SARPS (Standards and Recommended Practices) for each area of ICAO responsibility are published in 19 Annexes. Each Annex deals with a particular subject area and is subject to regular amendments. The details of many of them are contained in publications in the numbered ICAO Document Series.
 The ICAO Documents cover a range of matters from regulations to guidance. Some are available to the public without charge while others are only obtainable at a fee.
Description of ICAO Annexes ICAO link
Description of ICAO Annexes ICAO DOC link
Documents and Annex "examples" for ATC services and personnel:
Annex 2 – Rules of the Air
Annex 3 – Meteorological Service for International Air Navigation
Annex 10/II – Aeronautical Telecommunication, Volume II (Communication Procedures)
Annex 11 – Air Traffic Services
Annex 14 - Aerodromes
Doc 4444 – PANS-ATM - Air Traffic Management – Procedures for Air Navigation Services
Doc 7030/4 – Regional Supplementary Procedures.
ICAO Doc 4444 (air traffic management)]
**EASA (EU AVIATION SAFETY AGENCY) **
EASA Supports its Member States in implementing those ICAO standards, for example through the compliance checklists (CC) (details on EASA webpage).

The CCs show the status of implementation of ICAO Standards and  Recommended Practices (SARPs) in a particular State, as well as any differences that may exist between the national/European regulations and the ICAO SARPS

EASA started with eRules project..

EASA eRules will be a comprehensive, single system for the drafting, sharing and storing of rules. It will be the single source for all aviation safety rules applicable to European airspace users. It will offer easy (online) access to all rules and regulations as well as new and innovative applications such as rulemaking process automation, stakeholder consultation, cross-referencing, and comparison with ICAO and third countries’ standards.


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What is the difference between a loss of control and an upset?
What is the difference between a loss of control and an upset? From what I have read, first, an upset occurs, which leads to a loss of control (LOC). But, when can one say that the upset has been transformed into a LOC?

Aircraft upset

 is a dangerous condition in aircraft operations in
  which the flight attitude or airspeed of an aircraft is outside the
  normal bounds of operation for which it is designed. This may result
  in the loss of control (LOC) of the aircraft, and sometimes the total
  loss of the aircraft itself.

Loss of control

 is the unintended departure of
  an aircraft from controlled flight, and is a significant factor in
  several aviation accidents worldwide and the leading cause of jet
  fatalities worldwide. Loss of control may be the result of
  mechanical failure, external disturbances, aircraft upset conditions,
  or inappropriate crew actions or responses.

TL;DR:

Upset occurs when attitude and/or airspeed are outside of the boundaries where the aircraft is controllable.
Upset is one of many possible causes for loss of control.

Or in short: upset = you're inverted (could be fun in certain aircraft), loss of control = you can't get back upright.

@Jan, upset is not inverted, and inverted is not an upset in aircraft that are designed for it.


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How to define quarter-chord sweep angle for a cranked wing?
I have the values for surface area, span, aspect ratio, and quarter chord sweep angle, etc., for a general trapezoidal planform. So, I changed my wing to a single cranked wing such that surface area and span doesn't change. Therefore, parameters like root chord, tip chord, etc., changed. Now, for the, cranked wing how to define quarter-chord or half-chord sweep angles?

I think adding a drawing of your wing can help mental representation.

I think you have to define the sweep angles for every section on the cranked wing. You can use the same definition for each segment as for a "normal" wing. So practically speaking: Root Segment quarter chord --> create line between quarter chord of root and quarter chord of kink. Then you can measure the sweep angle of the root segment. Continue with next segment. The quarter-chord sweep angle is the angle between the y axis and the quarter chord line.

So, one cannot define the quarter chord sweep angle for the whole cranked wing?

Of course you can do it, but what would you do with that? Usually you are using these parameters for aerodynamic analysis, so you have to analyze every panel seperately. For example the Drag Divergence Numbers for each Panel. When do they become supersonic and how does the neutral point shift in the transonic/supersonic regime etc.

Okay got it. Thanks!


text:
When were commercial pilots first allowed to use glasses?
Currently, pilots with defective (but correctable) vision are allowed to pilot airliners if they have at least two pairs of their corrective lenses (typically glasses) with them on board.
Was there a specific moment in time when this was first allowed by law and regulations (prior to which persons with defective vision would have been prohibited from piloting an aircraft, even with corrective lenses)? Or has flying with corrective lenses been allowed since the earliest moments of airliners' history?

Airliner is not the same as commercial. Commercial may include banner towing and insecticide spraying. You may add which one interest you. Good question by the way.

Interesting question, although perhaps it's actually about when commercial pilots were first required to wear glasses? In the very early days of aviation more or less anything was allowed because there were no regulations anyway: the first US licenses were introduced in 1926 but passengers were paying for flights as early as 1914.

Thank you for your comments. Yes, I am referring to airliners (large passenger and cargo aircrafts serving commercial transportation services) and yes, I am referring to the moment when using glasses or other visual support devices were required. That's about clarification, because the good answer has already been provided.

In the US, the department of commerce had an Aeronautics Branch. It was first responsible for civil aviation safety. On February 28, 1927 it published a list of the first physicians, who were qualified to give medical examinations for pilot licenses.
On December 31, 1926, the Aeronautics Branch issued the first air commerce regulations, that included medical standards. These standards discerned three levels of physical standards one for each class of pilot : private, industrial and transport. The standards included regulations for visual acuity. Private and industrial class pilots were allow to wear corrective glasses.

Do you have a link to those original regulations? They'd make interesting reading.


text:
Statistically, how safe are para-motor craft compared to other GA planes?
I know there are very well kept records for death and accident rates in GA aircraft, but I was wondering if there were numbers for para-motor aircaft that are easy to compare?

What kind of statistics are you interested in? accident per flight? accident per flight hour? accident by distance covered?  absolute accident number? all of them?

In the US, there are no records kept nationally, because they fly under FAR Part 103, and are, for the most part, unregulated. Neither para-motors themselves, nor their pilots are required to be certified. Para-motors are not required to be registered. In fact, there is no actual government regulation requiring training of any kind to fly a para-motor. It is recommended, but not actually required.
There is no requirement to report accidents to any governing body, beyond those of the organization (flying club) the pilot may belong to.
Pilot certification -

At this time, however, pilots of ultralight vehicles are not required by Federal regulation to be certificated.

Aircraft Certification -

However, the FAA presently has no intent to require certification of these vehicles by Federal regulation.

Aircraft Registration -

However, registration of ultralight vehicles will not be required by Federal regulation at this time.

You are correct. Class E is controlled not the same as Class G. You are not, however, required to report in to anyone in either G or E. Just that while in E you must have visibility of 3 miles. My bad, and it was incorrect information. I have simply removed it. It's not really relevant to the question asked. Up- or Down-vote as you wish. My gist was that since neither the pilots nor the aircraft are required to be registered, it would be difficult to maintain records of accidents.


text:
Orange object on back of jet-engine pylons, what is it?
Watching this Video of a L-1011, I noticed an orange/brown object on the back of the jet-engine pylons I never saw before.

What is it?
What's the purpose of it?

It looks like a simple infrared jammer as in this image, but seems strange on an airline

@ManuH maybe a former military craft that never had the thing refitted

Great catch! I don't know if I'd have ever noticed it.

Probably "rachet freak" is right, the 747 seen later in the video doesn't have one fitted.

Manu H is right. It is an IR jammer device. Saudi (corrected from the comment of David Richerby:)Royal Flight airliners tend to have them (root of the wing, next to the light)...

That is one of the nicest SP photos that I've ever seen! I just sat there staring at it for a few minutes... the angle and zoom really emphasize the muscular attributes of the 747 fuselage. Magnificent!

The photo you link to is a 747SP that's part of the Saudi Royal Flight so might be expected to have more defensive equipment attached than your average airliner. For example, this Saudia 747 doesn't seem to have jammers at the wing root; likewise, this Saudia freighter.

@David Richerby, you're right I also recognized that, so the Mistery remains.

Now I see, the Royals used a L-1011 before they bought the 747SP. I always thought that what I saw in the video was a commercial aircraft.
http://www.airliners.net/aviation-forums/general_aviation/read.main/1739630/

@DavidRicherby you linked twice the same photo

@Federico Oops. Too late to fix it now. The second one was supposed to be a head-on view of a 747 freighter that also didn't have the jamming device at the wing root but it's not worth the time it would take to find the right link again.

I think this is an infrared counter-measure device, i.e. a device intended to protect aircraft from "heat seeking" missiles. Saudi no doubt flies to some potentially dangerous spots in the Middle East.  See this article.


text:
Why were the TWA TriStar middle seats smaller than the aisle seats?
I was watching an old TWA advert and a question came up:
why were the L-1011 TriStar middle seats smaller than the aisle seats?

Probably to allow better viewing of the projector screen up front.

Its possible it was done only for this advertisement, since I can't find any interior shot with the same arrangement on Google images at least.

Those seats aren't smaller! TWA had fold over seatbacks, resulting in a nice table for the seat next to you if the flights weren't full. They are the exact same size as the other seats. Also, those things down the centerlines between the seats were coat closets.
Later replaced by a full width seat when they went from 2-4-2 to 2-5-2 in their last configurations.


text:
How does the fuel pump work in a PA-28 and when should I use it?
Just started flying again after 14 years and I'm taking this to the finish line this time. All my time, up till 10 am today, is in a C172. I did fly a PA 28-151 today and liked it.
I do have some questions about Pipers (specifically PA 28-181 and 28-151):

Does the fuel pump has to be on the entire flight?
Is there a fuel pump for each tank?
If the pump doesn't have to be on the entire flight, how does the engine/carburetor get fuel considering the engine is higher than the wings?

Welcome to aviation.SE! Whatever answers you get here, do check out the POH for that specific aircraft to make sure you have the correct systems information and procedures for it.

The PA-28 Family of aircraft have two fuel pumps, an engine driven mechanical pump that is always pumping (so long as the crank shaft is spinning) and is considered the "main pump". The airframe also has an electrical backup pump that can be actuated by the pilot. The tanks do not have their own pumps.
You should check the POH for your airframe but generally speaking in the Archer and Arrow I fly the electric fuel pump is turned on:

checking fuel pressure before start
during take off
climb out
when switching tanks (I also run it for 30 seconds after switching tanks incase I either need to switch back and to maintain fuel pressure at a critical time in the event of a failure of the mechanical pump)
on approach
landing/go-around
in the event of a mechanical pump failure
while practicing maneuvers (S-Turns, turns around a point ETC)
during a practice stall
Engine power loss in flight
Loss of fuel pressure

Most of the above items can be found in this POH.
Note: You should not be running the electric fuel pump for the entire flight, like anything this is a component that can burn out and it should be used when needed or dictated by the POH.

The  EDFP in Lycomings is pretty much an automotive pump as you'd see on cars in olden tymes before in-tank electric pumps. It might get a couple of extra inspections as an aircraft part, but it's otherwise identical.  I just installed a cooling shroud on my pump, since I run my O-290 on auto fuel.  The pump is run by a little push rod that is driven by an eccentric cam in the accessory case, and the rod works the pump lever.

I was also trained to turn on the electric fuel pump before starting any maneuvers.it should be part of your pre-maneuver checklist along side doing clearing turns.

Yeah, as a long-time PA-28 pilot, I would also say before manoeuvres (stall practice, steep turns etc) too. Otherwise great answer!

The electric pumps on Pipers and Cessna Cardinals are Facet solenoid-piston pumps (the dika-dika-dika sound is the magnetically driven piston sliding back and forth) that pretty much run forever and can't overheat, so while not advisable, it's not too big a deal to accidentally leave it on.  Some homebuilts use two of them instead of an EDP and one of the electric pumps runs full time with the other as backup.

Thank you Dave for giving me a fish (the answer to my question) AND showing me how to fish (POH). You're AWESOME

@JohnK That's good to know because on more than one occasion I have been distracted and forgotten to switch it off during my ToC checks on departure. Sometimes for a whole flight!

One last consideration that may or may not be universally applicable:  I've seen my fuel flow go up dramatically with the backup fuel pump on in my Long EZ.  That may be a consideration in other aircraft re:forgetting to turn it off.


text:
Why are the best glide and best range airspeeds different for a C172?
According to Cessna 172 POH the speed for max range with power off, or glide speed, is 65, and achieved at the best L/D ratio.
However with power on the speed for max range will be around 75.
Why is there a difference between speeds for max range with and without power?
Edit-
Is this because with power off we are just looking for the lowest point on the drag curve, and with power on we are willing to accept the increase in drag from speed of 65 to 75 since I guess lift increases more then drag between those speeds?

Different vertical speeds and altitudes?

Because max range isn't the same as max endurance. See this question: https://aviation.stackexchange.com/questions/36440/why-is-the-ratio-maximum-range-speed-maximum-endurance-speed-the-same-for-any-ai/36443#36443

A- what altitudes?
B- what does endurance have to do with anything? That wasn’t mentioned anywhere in the question

@leha007  Flying at best L/D will give you max endurance, but (as the linked Q/A explains) that isn't the same as max range. Regardless of the altitude you're at.

Ralph J- according to TC flight manual- “maximum range is achieved when the aircraft is being operated at the angle of attack giving the greatest ratio of lift to drag”. Maximum range- not maximum endurance.

What model and flap setting? My c172m manual says best glide at max weight is 80mph indicated (70kts ias) and 9:1 in calm air. Best fuel range is about 105mph/91kts ias. It would seem odd for newer models to be less aerodynamically efficient.

Maximum range depends not only on the variation of lift to drag versus airspeed, but also on the efficiency of the engine and propeller versus airspeed. The C172's fixed pitch prop, fixed ignition spark advance timing, fixed valve lift and closure timing and other characteristics all have effects on the miles per gallon attained at different indicated airspeeds along with the lift to drag of the airframe.